Apoptosis Of Peripheral Blood Leukocytes Research Articles

The Role of the Soluble Interleukin-6 Receptor in the Progression of Nonalcoholic Fatty Liver Disease.

The blood level of soluble IL-6 receptor was measured in patients with different clinical and morphological forms of nonalcoholic fatty liver disease and healthy donors. The relationship of the soluble IL-6 receptor with the content of IL-6, the level of the IL6 gene mRNA, and a number of markers of hepatocyte and peripheral blood leukocyte apoptosis was assessed. It has been established for the first time that progression of nonalcoholic fatty liver disease is associated with changes in the level of soluble IL-6 receptor in the blood. In patients with high activity of nonalcoholic steatohepatitis and liver cirrhosis, the blood concentration of soluble IL-6 receptor sharply decreased in comparison with the earlier stages of progression of nonalcoholic fatty liver disease (liver steatosis, nonalcoholic steatohepatitis of weak and moderate activity). This allows considering the decrease in this indicator as a new diagnostic marker for distinguishing nonalcoholic steatohepatitis of high activity from weak and moderate activity. A close correlation between changes in the level of soluble IL-6 receptor and apoptosis of peripheral blood leukocytes and hepatocytes was revealed.

Radioprotective Effects of Combined Melatonin and Famotidine Treatment on Radiation Induced Apoptosis in Peripheral Blood Leukocytes of Breast Cancer Patients and Normal Individuals.

Objective The aim of this study was to evaluate the effects of individual or combined use of two antioxidants, melatonin and famotidine on radiation induced apoptosis in leukocytes from breast cancer (BC) patients. Materials and Methods In this experimental study, the DPPH assay was used to determine the appropriate doses of melatonin and famotidine for treatment of BC and control leukocytes. The leukocytes were cultured in complete RPMI- 1640 medium and treated with either agent for two hours. Cells were exposed to 4 Gy gamma rays generated from a Co-60 source at a dose rate of 0.85 Gy for 48 hours before harvesting. The cells were placed on slides and the neutral comet assay was performed. A total of 500 cells were stained with ethidium bromide and assessed for the amount of apoptosis under a fluorescent microscope x400 magnification. Results We observed significantly more apoptosis following radiation alone in the leukocytes from BC patients compared with normal individuals (P<0.01). Individual use of famotidine and melatonin induced very low frequencies of apoptosis that was not significantly different from the control (P>0.05). However, when combined with radiation, there was a decreased frequency of apoptosis in leukocytes of both normal and BC patients (P<0.05). The effect of famotidine was more pronounced than melatonin. ConclusionMelatonin, despite its potent antioxidant property, does not significantly affect radiation induced apoptosis in leukocytes derived from normal individuals; however, it has a moderately significant protective effect on in leukocytes derived from BC patients. Therefore, when used with radiation it might not intervene with the radiotherapy (RT) regimen of BC cancer patients. Famotidine is a good radioprotector for normal tissue. However, the efficacy of RT might be reduced with an accumulation of famotidine in tumour tissues.

Emodin attenuates CY-induced oxidative injury in PBLs of the blunt snout bream (Megalobrama amblycephala) though the Nrf2-Keap1 signaling pathway

The present study aimed to evaluate the protective effects of emodin on cyclophosphamide (CY)-induced oxidative injury in peripheral blood leukocytes (PBLs) of blunt snout bream and the potential mechanisms. We examined the cell viability, lactate dehydrogenase (LDH) release, apoptosis, mitochondrial membrane potential (Δѱm), reactive oxygen species (ROS) generation and correlative gene expression of nuclear factor-erythroid 2 related factor-2 (Nrf2)-Kelch-like ECH-associated protein 1 (Keap1) signaling molecules. For the control group, PBLs were maintained in normal cell culture medium for 12 h. For the CY group, cells were exposed to 0.32 mg/mL CY for 6 h, followed by maintaining in RPMI-1640 complete medium for an additional 6 h. Cells in the CY + Emodin group were exposed to 0.32 mg/mL CY for 6 h, and then exposed to 0.20 μg/mL emodin for 6 h. We observed that emodin significantly inhibited CY-induced apoptosis in PBLs through increasing cell viability and decreasing LDH release. Emodin also inhibited Δѱm disruption and respiratory burst in CY-induced PBLs. In consistent with these results, emodin attenuated oxidative stress in CY-induced PBLs by significantly upregulating Nrf2, BTB and CNC homolog 1 (Bach1), superoxide dismutase (SOD) and catalase (CAT) genes while significantly downregulates Keap1 in Nrf2-Keap1 signaling pathway. These results collectively demonstrate that emodin can alleviate CY-induced oxidative stress in the PBLs of blunt snout bream, possibly through activating Nrf2-Keap1 signaling pathway. Our findings also suggest that emodin might be developed as a promising therapeutic agent for treating oxidative injury in blunt snout bream.

Molecular characterization, expression analysis and function identification of Pf_TNF-α and its two receptors Pf_TNFR1 and Pf_TNFR2 in yellow catfish (Pelteobagrus fulvidraco)

Inflammation is a common manifestation of body immunity and mediates a cascade of cytokines. Tumor necrosis factor-α (TNF-α), as a multi-effect cytokine, plays an important role in the inflammatory response by interacting with its receptor (TNFR). In this study, Pf_TNF-α, Pf_TNFR1 and Pf_TNFR2 genes were cloned from yellow catfish (Pelteobagrus fulvidraco), and bioinformatics analyses showed that the three genes were conserved and possessed similar sequence characteristics as those of other vertebrates. The qPCR results showed that Pf_TNF-α, Pf_TNFR1 and Pf_TNFR2 mRNAs were constitutively expressed in 14 tissues and the lymphocytes of four tissues from healthy adults. The mRNA expression levels of Pf_TNF-α and Pf_TNFR1 genes were significantly up-regulated in the spleen, liver, trunk kidney, head kidney and gill after Edwardsiella ictaluri infection, while the mRNA expression of Pf_TNFR2 was significantly up-regulated in the spleen, and down-regulated in the liver and gill. In the isolated peripheral blood leukocytes (PBLs) of yellow catfish, the expression of Pf_TNF-α mRNA was notably up-regulated and the two Pf_TNFR transcripts were distinctly down-regulated after stimulation with lipopolysaccharides (LPS), peptidoglycan (PGN), polyinosinic-polycytidylic acid (Poly I:C) and phytohaemagglutinin (PHA). After stimulated by recombinant (r) Pf_sTNF protein, the mRNA expressions of various inflammatory factors genes were up-regulated in the PBLs. Meanwhile, rPf_sTNF promoted the phagocytic activity of leukocytes, whereas the activity mediated by rPf_sTNF could be inhibited by rPf_TNFR1CRD2/3 and rPf_TNFR2CRD2/3. The up-regulation of TNF-α and IL-1β mRNAs expression triggered by rPf_sTNF could be inhibited by MAPK inhibitor (VX-702) and NF-κB inhibitor (PDTC). rPf_sTNF induced the expression of FADD mRNA in PBLs and increased the apoptotic rate of PBLs, and inhibiting the NF-κB and MAPK signal pathways could enhance the apoptosis of PBLs. The results indicate that Pf_TNF-α, Pf_TNFR1 and Pf_TNFR2 play important roles in the immune response of yellow catfish to bacterial invasion.

Tongue sole (Cynoglossus semilaevis) interleukin 10 plays a negative role in the immune response against bacterial infection

Interleukin-10 (IL-10) is a pleiotropic cytokine and plays a crucial role in immunity. In the current study, we examined the expression patterns and biological functions of tongue sole Cynoglossus semilaevis IL-10 (CsIL-10). CsIL-10 is composed of 186 amino acid residues and shares 46.3%–71.7% identities with other teleost IL-10. Csil-10 expression occurred in multiple tissues and was regulated by bacterial infection. Recombinant CsIL-10 (rCsIL-10) in the form of a dimer bound to a wide range of bacterial species but did not affect bacterial growth. rCsIL-10 could interact with peripheral blood leukocytes (PBL) and significantly reduce the phagocytic activity, ROS production, and apoptosis of PBL. When injected in vivo, rCsIL-10 significantly suppressed the expression of proinflammatory cytokines and promoted bacterial dissemination in tongue sole tissues. Consistently, knockdown of Csil-10 significantly inhibited bacterial infection in tongue sole. Taken together, these results indicate that CsIL-10 plays a negative regulatory role in the immune response against bacterial infection.

Clinical and laboratory correlation in patients with consequences of traumatic brain injury

The aim of this study was to establish main peculiarities of apoptosis of peripheral blood leukocytes in patients with traumatic brain injury consequences of varying severity under conditions of disease progression Methods . In 220 patients with the effects of light (71), moderate (59) and hard (90) TBI and the catamnesis of trauma in the age from 1 to 30 years percentage of peripheral blood leukocytes in stage of apoptosis (ANV +) and necrotic (PI +) and the level of reactive oxygen species (ROS +) was explored by flow cytofluorometry method. The control group consisted of 30 people representative by age and sex. Neurological status was assessed by Neurological Outcome Scale for Traumatic Brain Injury (NOS-TBI), cognitive status - Montreal scale for cognitive deficit (Mosa), the level of anxiety and depression – by the HADS scale Results. Patients with TBI consequences of varying severity established significant growth indicators characterizing the level of necrosis and apoptosis of peripheral blood leukocytes, and increase the percentage of cells containing active oxygen species. Reliable dependence of indicators RI + ANV + peripheral blood leukocytes and ROS + on patient's age, duration and type of injury was not found Conclusions. Conditioned upon progression of neurological deficit (accession of extra-pyramidal symptoms, occurrence and progression of cognitive disorders, etc.) significantly higher values RI + ANV + peripheral blood leukocytes and ROS + were found

Immune effects of R848: Evidences that suggest an essential role of TLR7/8-induced, Myd88- and NF-κB-dependent signaling in the antiviral immunity of Japanese flounder (Paralichthys olivaceus)

The imidazoquinoline compound R848 is a specific agonist of toll-like receptor (TLR) 7/TLR8 that has been used as an immunostimulant in humans against viral diseases. Although R848-induced immune response has been reported in teleost fish, the relevant mechanism is not clear. In this study, we investigated the antiviral potential and the signaling pathway of R848 in a model of Japanese flounder (Paralichthys olivaceus). We found that R848 was able to inhibit the replication of megalocytivirus, stimulated the proliferation of peripheral blood leukocytes (PBL), enhanced the expression of immune genes, and reduced apoptosis of PBL. When endosomal acidification was blocked by chloroquine (CQ), R848-mediated antiviral activity and immune response were significantly reduced. Likewise, inhibition of Myd88 activation markedly impaired the pro-proliferation and anti-apoptosis effect of R848. Cellular study showed that cultured founder cells treated with R848 exhibited augmented NF-κB activity, which, however, was dramatically reduced in the presence of CQ and Myd88 inhibitor. Furthermore, when NF-κB was inactivated, the effect of R848 on cell proliferation and apoptosis was significantly decreased. Taken together, these results indicate that R848 is an immunostimulant with antiviral property in a teleost species, and that the immune response of R848 is mediated by, most likely, TLR7/TLR8 signaling pathway, in which Myd88 and NK-κB play an essential role.

Apoptosis of peripheral blood leukocytes from rabbits infected with non-haemagglutinating strains of rabbit haemorrhagic disease virus (RHDV)

The report demonstrates that the induction of apoptosis in peripheral blood granulocytes and lymphocytes of rabbits infected with three non-haemagglutinating RHDV strains (English Rainham, German Frankfurt, and Spanish Asturias) is a crucial determinant of the pathogenesis of rabbit haemorrhagic disease. Apoptosis was measured by flow cytometric detection of caspase activity. These studies demonstrated that the investigated RHDV (rabbit haemorrhagic disease virus) viral strains affected leukocyte apoptosis to varying degrees. Enhanced leukocyte apoptosis was detected between 4 and 36h after infection and was more pronounced in lymphocytes than in granulocytes. The data presented here thus provide a preliminary understanding of the kinetics of apoptosis in leukocytes of rabbits infected with RHDV.

The role of apoptosis in immunosuppression of dogs with demodicosis

The aim of the present study was to evaluate the status of apoptosis in peripheral blood leukocytes of dogs with demodicosis. A total of 26 dogs suffering from demodicosis, and positive for Demodex canis mites by skin scraping, participated in the study, 13 with localized demodicosis (LD) and 13 with generalized demodicosis (GD). A further 13 clinically healthy dogs, all of whom were negative for mites upon skin scraping, were used as controls. The dogs with GD revealed significantly higher ( P ≤ 0.0001) percentage of leukocytes with externalization of phosphatidylserine (PS) and depolarized mitochondrial membrane potentials (Δ Ψm) as compared with the dogs with LD and healthy controls. These dogs also revealed significantly lower values ( P ≤ 0.0001) of hematological parameters viz. hemoglobin, total erythrocytes count total leukocytes count, lymphocytes, monocytes and neutrophils. Significantly higher ( P ≤ 0.0001) percentages of leukocytes with externalization of PS and depolarized Δ Ψm were also found in dogs with LD as compared with the healthy controls. These dogs also revealed significantly lower values of Hb ( P ≤ 0.0001), TEC ( P = 0.025), TLC ( P ≤ 0.0001), lymphocytes ( P = 0.008), monocytes ( P ≤ 0.0001) and neutrophils ( P = 0.03). It is concluded that premature apoptosis of PBL may be implicated in the immunosuppression of the dogs with demodicosis.

Leukocyte apoptosis and pro-/anti-apoptotic proteins following downhill running

The purposes of this study were to determine the effect of eccentric exercise-induced muscle damage on the induction of apoptosis in peripheral blood leukocytes and to investigate if the elevation in apoptotic leukocytes was mediated by changes in the concentration of anti-/pro-apoptotic proteins in circulation. Twelve moderately trained subjects performed three 40 min treadmill runs at ~70% VO(2max): a level run (L) followed by two downhill runs (DH1 and DH2). Blood samples were taken at rest (PRE) and immediately (POST), 2, 24, and 48 h after each run. Data were analyzed using two-way repeated measures analysis of variance with post hoc Tukey tests. Creatine kinase (CK) activity was significantly elevated at 24 and 48 h following DH1 (P < 0.01). The proportion (%) of apoptotic leukocytes was significantly elevated at POST and 2 h following all three runs, and up to 48 h following DH1 (P < 0.01). Bax at 24-h post and Bax/Bcl-2 ratio at 24- (P < 0.01) and 48-h post (P < 0.05) following DH1 were greater than PRE (P < 0.05). An acute bout of moderate intensity downhill running altered CK activity, Bax concentration and the Bax/Bcl-2 ratio in circulating leukocytes resulting in a greater apoptotic response at 24- and 48-h post-exercise compared to level grade running or a second downhill run. Although the mechanism by which these proteins are altered by unaccustomed eccentric exercise is currently unknown, the differential response to DH1 versus L and DH2 indicates that it may be related to exercise-induced muscle damage.

Determination of oxidative status and apoptosis in peripheral blood of dogs with sarcoptic mange

The aim of the present study was to determine the erythrocytic oxidant/antioxidant balance and apoptosis of peripheral blood leukocytes of dogs with natural Sarcoptes scabiei var. canis mite infestation. A total of twenty four clinically Sarcoptes-infested dogs were examined and used to execute the study. While another twenty four healthy dogs free of any ecto-parasite were used as controls. Peripheral blood samples were obtained from each infested only once on the day of dermatological examinations. Determination of oxidant/antioxidant balance was conceded by estimating the levels of lipid peroxides and antioxidants in erythrocytes. While, apoptosis of peripheral blood leukocytes was determined by estimating externalization of phosphatidylserine (PS) at the cell surface as well as by detection of depolarization mitochondrial membrane potential (Δ Ψm) by flow cytometry. Sarcoptes-infested dogs had revealed significantly higher ( P ≤ 0.001) contents of erythrocytic lipid peroxides in comparison with the healthy controls. Whereas the level of reduced glutathione was found to be significantly lower ( P ≤ 0.001) in Sarcoptes-infested dogs as compared to the healthy dogs. The activity of glutathione peroxidase was found to be significantly lower ( P ≤ 0.001) in Sarcoptes-infested dogs as compared to the healthy dogs. The activity of glutathione-S-transferase was also found to be significantly lower ( P ≤ 0.001) in Sarcoptes-infested dogs as compared to the healthy dogs. The dogs with sarcoptic mange had revealed significantly lower ( P ≤ 0.001) activity of superoxide dismutase in coparision with the healthy dogs. The dogs with sarcoptic mange had also revealed significantly lower ( P ≤ 0.001) activity of catalase in coparision with the healthy dogs. The percentage of apoptotic leukocytes was found to be significantly higher ( P ≤ 0.001) in Sarcoptes-infested dogs as compared to the healthy controls. Sarcoptes-infested dogs had also exhibited significantly ( P ≤ 0.001) higher percentage of leukocytes with depolarized mitochondrial membrane potential in comparison with the healthy controls. It is concluded that significant alteration in oxidant/antioxidant balance and increased rate of apoptosis in peripheral leukocytes may be implicated in the pathogenesis of clinical Sarcoptes mite infestation in dogs.

Ocorrência de apoptose em leucócitos no esfregaço de sangue periférico e em sincícios na infecção in vivo pelo vírus da cinomose canina

The aim of this paper is to report the occurrence of apoptosis in peripheral blood leukocytes and in syncytia induced by experimental infection of dogs with canine distemper virus. Blood was collected from nine puppies that were inoculated with the Snyder Hill strain of CDV, and stained with May Grunwaldt-Giemsa. Dogs were necropsied and retropharyngeal lymph nodes were collected and processed for paraffin embedding. Five micrometers thick sections were stained with hematoxylin-eosin and methyl green pyronin. Other sections were submitted to TUNEL reaction for in situ detection of apoptosis, and immunohistochemistry to detect CDV antigen. Immunohistochemistry confirmed the presence of viral antigen. Syncytia were present in all retropharyngeal lymph nodes. Several syncytia contained apoptotic nuclei as detected by hematoxylin-eosin and methyl green pyronin stains. Apoptotic nuclei were labeled inside syncytia by the TUNEL reaction. Blood smear analyses indicated higher proportion of apoptotic leukocytes in the peripheral blood of infected dogs.

Glucocorticosteroid therapy in optic neuritis and multiple sclerosis. Evidence from clinical studies and practical recommendations

High-dose intravenous glucocorticosteroids (GS) are the treatment of choice for acute relapses in patients with multiple sclerosis. We review the evidence from published trials on GS treatment in MS. Several controlled clinical trials have proven the efficacy of high-dose GS in accelerating the recovery from acute attacks. With serial MRI recordings, a reduction in the number of enhancing lesions has been observed after high-dose GS treatment. Definitive long-term effects of GS on disease evolution could not been demonstrated. There is now evidence that ultra-high doses of GS might be superior in comparison to standard pulse treatment regarding relapse rate and disease progression. In experimental autoimmune encephalomyelitis (EAE), an animal model for some features of MS, doses of up to 50 mg/kg methylprednisolone markedly augmented T cell apoptosis in situ, leading to a faster clearance of inflammatory infiltrates. Apoptosis in peripheral blood leukocytes could also be detected after i.v. GS treatment in MS patients. In a recent MRI study, ultra-high doses of GS were significantly more effective in reducing contrast-enhancing lesions and in maintaining blood-brain barrier integrity after a clinical relapse. Further clinical trials are necessary to study the long-term effects of ultra-high doses of GS on disease progression and disability.

High-Dose Methylprednisolone Therapy in Multiple Sclerosis Induces Apoptosis in Peripheral Blood Leukocytes

Apoptosis is supposed to contribute to the elimination of T cells from the inflamed central nervous system in the natural disease course of multiple sclerosis (MS). In the animal model experimental autoimmune encephalomyelitis, T-cell apoptosis can be induced by high-dose glucocorticoid (GC) administration. To study the effects of intravenous high-dose GC therapy in MS on T-cell apoptosis ex vivo. Sixty-six patients with MS (28 with relapsing-remitting MS, 22 with secondary chronic progressive MS, and 16 with primary chronic progressive MS) and 16 control patients receiving corticosteroids for other disorders were included in the study. Blood samples were collected before and immediately after the first infusion of 500 to 1000 mg of methylprednisolone given during 2 hours in the early morning. Gradient-isolated peripheral blood leukocytes (PBLs) were cultured, unstimulated, with corticosteroids (positive control), the mitogen phytohemagglutinin, or anti-T-cell receptor monoclonal antibody. For investigation of apoptosis, PBLs were cultured overnight and analyzed by immunoflow cytometry using TUNEL (terminal transferase-mediated dUTP biotin nick end labeling) or annexin labeling in combination with CD4, CD8, CD22, CD56, or bcl-2 staining. Proliferation was measured by (3)H-thymidine incorporation. For cytokine determination, supernatants were collected after 48 hours of culture. After in vivo corticosteroid treatment, apoptosis of unstimulated PBLs was markedly and significantly augmented in all 3 MS subgroups. Fluorescence-activated cell sorter analysis showed that apoptosis affected predominantly CD4 T cells. Natural killer cells showed a relative increase after GC therapy without a change in the rate of apoptotic cells. Expression of bcl-2 in T-cell subpopulations was not significantly modified by high-dose GC therapy. Culture supernatants of T-cell receptor-stimulated PBLs after GC therapy contained lower concentrations of interleukin 2, interferon gamma, and tumor necrosis factor alpha than those from PBLs taken before pulse therapy. Similar changes in the rate of apoptosis and cytokine production were seen in controls. Corticosteroid pulse therapy is a strong inducer of leukocyte apoptosis. Induction of apoptosis might contribute to the down-regulation of T-cell activity and thereby terminate inflammation in the central nervous system.

Direct Detection of Apoptotic Cells in Peripheral Blood from Highly Pathogenic SHIV-Inoculated Monkey

Apoptosis in peripheral blood leukocytes (PBL) has been estimated by the enhancement of spontaneous apoptosis after in vitro culture, because apoptotic cells have not been observed directly in freshly isolated PBL in the course of HIV/AIDS. In monkeys infected with a highly pathogenic simian/human immunodeficiency virus (SHIV), which corresponds to rapid progressors of HIV infection, a high frequency of apoptotic cells was directly detected in fresh PBL by electron-microscopic studies. Peripheral blood apoptosis transiently occurred after intense plasma viremia, and peaking at 3 weeks postinfection; occurrence was not limited specifically to lymphocytes, but also occurred in other types of leukocytes. Apoptosis in peripheral lymph nodes was also detected following intense plasma viremia. However, the in vivo apoptosis was not detected in nonpathogenic SHIV-infected monkeys that showed no cell loss. Thus, we directly showed the apoptosis of PBL, which might be associated with pathogenic SHIV produced during the time of plasma viremia.

Critical Role of Nitric Oxide During the Apoptosis of Peripheral Blood Leukocytes from Patients with AIDS

Highly active antiretroviral therapies (HAART) increase the CD4(+) cell count, but complete normalization of this parameter has not been obtained in some patients. As oxidative stress plays an important role during human immunodeficiency virus type 1 (HIV-1)-associated dementia and lymphocyte apoptosis, we asked whether the nitric oxide (NO) pathway plays a role in the in vitro survival of peripheral blood mononuclear cells (PBMC) from HIV-1(+) patients and how it correlates with peripheral CD4(+) cell levels. PBMC were isolated from patients with AIDS and assayed for apoptosis and proliferation in the presence of various chemicals, including agonists or antagonists of the NO pathway. Data were then compared with several in vivo parameters from the same patients. Apoptosis of PBMC in the presence of exogenous NO is significantly higher in patients with low peripheral CD4(+) cell levels than in patients with high CD4(+) cell numbers or seronegative individuals. In addition, endogenous NO inhibition rescues cells from apoptosis in AIDS patients with low circulating CD4(+) cell numbers and helps recovery of the T cell proliferative response. NO-mediated apoptosis does not require cGMP but involves peroxynitrite generation, PARP activation, and NAD(+) depletion. Taken together, the data suggest the involvement of NO during the apoptosis and functional impairment of lymphocytes in patients with AIDS.

Implication of Ectocytosis in IL-2 Receptor Expression, Proliferation, and Apoptosis of Human Leukocytes.

Shedding of plasma membrane or ectocytosis is a ubiquitous process in eukaryotic cells. In this study, we examined the role of vesicles exfoliated from human peripheral blood leukocytes (PBL) in proliferation, expression of IL-2 receptor (CD25) and in the process of apoptosis (programmed cell death) in these cells. Vesicles derived from peripheral blood leukocytes stimulated with conconavalin (Con)-A induced agglutination, IL-2 receptor expression and proliferation in leukocytes freshly isolated from peripheral blood in a fashion similar to that induced by Con-A. These vesicles expressed Con-A on their surface. Furthermore, IL-2 receptor expression induced by concanavalin-A and by vesicles derived from Con-A activated PBL was inhibited by an antiserum to Con-A suggesting that the activation induced by vesicles is mediated by Con-A bound to their membranes. In contradistinction to these vesicles, those derived from IL-2 activated PBL, induced apoptosis in PBL freshly isolated from peripheral blood. The apoptotic leukocytes were identified by loss of cell viability, their distinct morphologic characteristics, and by reactivity with the monoclonal antibody, BM1 that reacts with apoptotic cells. These studies implicate vesicles shed from leukocytes in the proliferation, expression of IL-2 receptor and apoptosis of leukocytes.